[PATCH v2 1/2] sched: Add cond_resched_rcu_lock() helper

To: Eric Dumazet <eric.dumazet@xxxxxxxxx>, Julian Anastasov <ja@xxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Subject: [PATCH v2 1/2] sched: Add cond_resched_rcu_lock() helper
Cc: lvs-devel@xxxxxxxxxxxxxxx, netdev@xxxxxxxxxxxxxxx, netfilter-devel@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>, Dipankar Sarma <dipankar@xxxxxxxxxx>, Simon Horman <horms@xxxxxxxxxxxx>
From: Simon Horman <horms@xxxxxxxxxxxx>
Date: Tue, 30 Apr 2013 11:52:57 +0900
This is intended for use in loops which read data protected by RCU and may
have a large number of iterations.  Such an example is dumping the list of
connections known to IPVS: ip_vs_conn_array() and ip_vs_conn_seq_next().

The call to cond_resched() is guarded by #ifndef CONFIG_PREEMPT_RCU as in
the case of CONFIG_PREEMPT_RCU _rcu_read_unlock() will check to see if the
RCU core needs to be informed, so there is no need to invoke cond_resched()
in that case. Thanks to Paul E. McKenney for explaining this.

cond_resched_rcu_lock() suggested by Eric Dumazet.
ifndef guard suggested by Paul E. McKenney and Julian Anastasov.

Cc: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Julian Anastasov <ja@xxxxxx>
Acked-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Simon Horman <horms@xxxxxxxxxxxx>


* Add guard the call to cond_resched()
 include/linux/sched.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index e692a02..66da71c 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2787,3 +2787,14 @@ static inline unsigned long rlimit_max(unsigned int 
+static void inline cond_resched_rcu_lock(void)
+       if (need_resched()) {
+               rcu_read_unlock();
+               cond_resched();
+               rcu_read_lock();
+       }

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